This application claims the priority of German Patent Application, Serial No. 101 46 523.8, filed Sep. 21, 2001, pursuant to 35 U.S.C. 119(a)-(d), the subject matter of which is incorporated herein by reference.
The present invention relates, in general, to a drive control system for a multiphase motor powered by a power converter.
Drives for high velocities or rotation speeds are increasingly in commercial use. This is true in particular for the power tool industry. Although rotation speeds of up to 20,000 rpm have already been employed and proven reliable, there is a need for rotation speeds in excess of 20,000 rpm. In particular, when high speeds are involved, motors feed back energy into the system. This is normally realized by a power converter on the mains systems side to feed energy back to the power supply. In case of trouble or a power outage, this energy cannot be fed back, resulting, especially in cases when motors are involved that rotate at high rpm, in significant overvoltages in the voltage intermediate circuit of a converter, which is connected before the motor, and may ultimately lead to the destruction of the converter.
To address this problem, the incorporation of a module has been proposed to reduce encountered overvoltage. A module of the type concerned here is illustrated in FIG. 1 and designated by reference numeral 2. The module 2, also called voltage-protection module (VPM), is placed between the input side of a multiphase motor 4 and the output side of a power converter 6 of a converter 8. In addition, the module 2 is connected via a control line 10 to the output side of a drive control system 12 of the motor-side power converter 6. The converter 8 includes a voltage intermediate circuit to electrically connect on the DC voltage side the power converter 6 on the motor side and a power converter 14 on the mains systems side. For sake of simplicity, the voltage intermediate circuit is not shown in detail. The power converter 14 on the mains systems side is implemented as a converter that is capable to feed back electric energy so as to enable a return of energy into the power mains supply 16 during braking action of the motor 4.
An overvoltage-monitoring device checks whether a determined actual voltage value of the voltage intermediate circuit of the converter 8 exceeds a predetermined limit value. As soon as an unacceptable overvoltage is occurs, module 2 is activated and drive control system 12 transmits control signals via the control line 10. The module 2 has incorporated therein a connection of at least several controllable power semiconductor switches, which can be switched off or disabled and are so controlled and switched together as to short the motor lines that are electrically connected via an electric path through the module 2. Optionally, the module 2 may also include resistors so that the electric loss power does not occur solely across the power semiconductor switches.
The provision of such a module 2 suffers shortcomings because the module 2 requires space which is approximately the same as the space needed for the motor-side power converter 6. Moreover, the module 2 has to be connected on the power supply side with the output side of the motor-side power converter 6 and the input side of the multiphase motor 2, and on the control side with the output side of the drive control system 12 of the power converter 6. This may lead to circuit failure.
A drive control system 12 of a type involved here is disclosed in European Patent Publication 0 742 637 and shown in more detail in FIG. 2. The multiphase motor 4 is connected in an electrically conductive manner with phase outputs L1, L2, L3 of the motor-side power converter 6. The power converter 6 includes six valve arms in the form of controllable converter valves or power semiconductor switches T1, T2, T3, T4, T5, T6, which can be switched off or disabled, whereby the power semiconductor switches T1, T3, T5 are arranged in the upper bridge side and the power semiconductor switches T2, T4, T6 are arranged in the lower bridge side. The power semiconductor switches T1, T2, T3, T4, T5, T6, are configured as insulated gate bipolar transistors (IGBT). Power semiconductor switches T1 and T2 of the upper and lower bridge sides of the power converter 6 form a bridge arm as do power semiconductor switches T3 and T4, and power semiconductor switches T5 and T6, and are connected between a positive busbar +Ud and a negative busbar xe2x88x92Ud of a voltage intermediate circuit, not shown in detail. The power semiconductor switches T1, T2, T3, T4, T5, T6 are each controlled by a electrically isolating device 18, of which only two are shown for ease of illustration. An example of such an electrically isolating device 18 includes optocoupler. By means of the electrically isolating devices 18, the power converter 6 (power component) is connected to the drive control system 12 (control component).
The drive control system 12 includes a control unit 20, e.g. a pulse width modulator, for providing signals to address the optocouplers 18 and thus to effect a switching of the semiconductor switches T1, T2, T3, T4, T5, T6 of the power converter 6. The signals are sent by the control unit 20 through three signal lines 17 for the upper bridge side and three signal lines 19 for the lower bridge side, whereby the signal lines 17, 19 include each a diode and a resistor in series. FIG. 2 illustrates, by way of example, the control for the two optocouplers 18, shown here. The drive control system 12 further includes a pulse suppressor 22 for cutting the energy supply to the electric drive by suppressing the pulses on the motor-side power converter 6. The pulse suppressor 22 is activated by a signal S1 and includes a further optocoupler for indicating the status of the pulse suppressor by means of a status signal SAKB which is sent to the control unit 20, on the one hand, as well as to a device 24 for braking by armature short-circuiting, referred to as xe2x80x9carmature short-circuit braking devicexe2x80x9d in the following description.
In the event of a fault, one of both bridge sides is blocked securely, while the other bridge side is switched on through timed control of the power semiconductor switches T2, T4, T6 so that at least two phases of the multiphase motor 4 are shorted. Of course, it is equally possible to block the lower bridge side and to provide a timed control of the upper bridge side of the power converter 6. In order to implement the required emergency braking in the event of a fault, the armature short-circuit braking device 24 now switches through all transistors T2, T4, T6 of the lower bridge side so that the three phases of the electric motor 4 are shorted across the negative busbar xe2x88x92Ud. The remaining kinetic energy of the multiphase motor 4 drives the braking current across the thus-realized shorted bridge. Through the timed control by means of a clock frequency, the power semiconductor switches T2, T4, T6 of the lower bridge side of the power converter 6 can be switched through in such a tailored manner that the braking moment generated by the short circuit can be appropriately varied. The armature short-circuit braking device 24 is intended for use solely in emergency situations to shut down the motor as quickly as possible.
It would therefore be desirable and advantageous to provide an improved drive control system, which obviates prior art shortcomings and is so configured as to omit the need for an external voltage-protection module.
According to one aspect of the present invention, a drive control system for a multiphase motor powered by a power converter of a type including a multi-pulsed bridge circuit with a plurality of controllable converter valves, which have an input side, and a plurality of electrically isolating devices in one-to-one correspondence with the converter valves, includes a control unit having an output side, wherein the input side of the converter valves is connected to the output side of the control unit via the electrically isolating devices; an armature short-circuit braking device constructed for connection with the input side of electrically isolating devices of one bridge side of the bridge circuit, an overvoltage recognition device having a first input terminal which receives a signal commensurate with a limit value, and a second input terminal which receives a signal commensurate with a determined actual input voltage of the power converter; and a trigger circuit having an output side which is connected to the armature short-circuit braking device, and an input side which is connected to an output side of the overvoltage recognition device and supplied with a signal for the armature short-circuit braking device.
The present invention resolves prior art problems by providing the drive control system with an overvoltage recognition device and a trigger circuit, whereby the trigger circuit links logically the output signal of the overvoltage recognition device with a trigger signal for the armature short-circuit braking device, so that the armature short-circuit braking device can be utilized also for drop of an overvoltage in the voltage intermediate circuit of the converter. A converter configured in this way contributes to a decrease in the number of components so that the overall drive system becomes more cost-efficient and reliable. Moreover, the need for assembly of an additional voltage-protection module is eliminated. In order to exploit the already existing armature short-circuit braking device for use as overvoltage protection in addition to the use as emergency shutoff, it is only necessary to incorporate the overvoltage recognition device and the trigger circuit. Thus, the operation of a voltage-protection module can be integrated with minimum expenditure in the drive control system of a converter.
According to another feature of the present invention, the overvoltage recognition device may be a comparator.
According to another feature of the present invention, the trigger circuit may be an OR gate.
According to another feature of the present invention, the control unit may be a pulse width modulator.
According to another feature of the present invention, the electrically isolating units may be an optocoupler.
According to another feature of the present invention, the converter valves may be insulated-gate bipolar transistors.
According to another feature of the present invention, the multiphase motor may *be a three-phase motor.
According to another feature of the present invention, the drive control system may be constructed in the form of a microcontroller.